The disclosed invention generally relates to center high mounted brake lights or stoplights for vehicles, and more particularly is directed to a stand-alone holographic center high mounted stoplight assembly that does not utilize the vehicle rear window to support the hologram structure of the stoplight assembly.
Present federal regulations require center high mounted stoplights in automobiles in addition to the traditional stoplights. The high mounted stoplights are intended to maximize the visibility of the stoplights to following drivers.
Center high mounted stoplights have been implemented as a standard red transmitting lenticular lens and an illuminating incandescent bulb enclosed in a housing that is commonly secured adjacent the top or bottom of an automobile rear window (also referred to as an automobile backlight). The bulky housing, which is intended to prevent scattered stoplight illumination from being within the driver's rearward field of view, partially obscures rearward visibility, imposes limitations on design, and is generally unattractive.
In order to avoid the visibility obscuration of the bulb and lens center high mounted stoplight, holographic stoplight systems have been developed wherein holograms secured to the automobile backlight provide stoplight illumination when illuminated with playback illumination. The holograms are substantially transparent to the driver's rearward field of view, and the playback illumination source is outside such field of view, which avoids the obscuration presented by the bulb and lens type stoplight assemblies. Examples of center high mounted holographic stoplight systems are disclosed in commonly assigned U.S. Ser. No. 07/000,793, filed Jan. 7, 1987 now U.S. Pat. No. 4,892,369 and U.S. Ser. No. 07/293,927, filed Jan. 4, 1989 now U.S. Pat. No. 4,916,593.
A consideration with known holographic stoplight systems in general is the utilization of the vehicle rear window to support the holographic structure of the system, which requires additional lamination processing and which requires adaption of the system for each different rear window configuration.
Further considerations with known holographic stoplight systems that utilize projected playback illumination include possible blockage by items placed in the rear of the vehicle, the possibility of objectionable reflections off the rear window, and objectionable heat from the light source. A further consideration with a holographic stoplight system that utilizes projected playback illumination is ambient turn-on, including turn-on that diffracts light into the vehicle operator's rearward field of view.
A further known holographic stoplight system couples playback illumination through the edge of the hologram, for example, by a fiber optic link, as disclosed in commonly assigned U.S. Pat. No. 4,892,369, issued Jan. 9, 1990. A consideration with an edge coupled system is the efficiency of the hologram and the use of a highly collimated, very narrow bandwidth playback illumination such as could be provided by a laser or very bright playback illumination.
Other considerations with known holographic stoplight systems include the complexity and difficult assembly of the optical elements.